lpr: add more accurate comments

*: trailing whitespace removal

editors/patch.c

@@ -136,7 +136,7 @@ int patch_main(int argc ATTRIBUTE_UNUSED, char **argv)
 		src_stream = NULL;
 
 		if (backup_filename && !stat(original_filename, &saved_stat)) {
-			src_stream = xfopen((strcmp(original_filename, new_filename)) ? 
+			src_stream = xfopen((strcmp(original_filename, new_filename)) ?
 							    original_filename : backup_filename, "r");
 		}
 

editors/vi.c

@@ -1718,7 +1718,7 @@ static int find_range(char ** start, char ** stop, char c)
 		p = t;
 	}
 
-	// backward char movements don't include start position 
+	// backward char movements don't include start position
 	if (q > p && strchr("^0bBh\b\177", c)) q--;
 
 	multiline = 0;

include/unarchive.h

@@ -14,7 +14,7 @@ typedef struct file_header_t {
 	char *name;
 	char *link_target;
 #if ENABLE_FEATURE_TAR_UNAME_GNAME
-	char *uname; 
+	char *uname;
 	char *gname;
 #endif
 	off_t size;

miscutils/chrt.c

@@ -67,7 +67,7 @@ int chrt_main(int argc ATTRIBUTE_UNUSED, char **argv)
 		fflush_stdout_and_exit(EXIT_SUCCESS);
 	}
 
-	argv += optind; 
+	argv += optind;
 	if (opt & OPT_p) {
 		pid_str = *argv++;
 		if (*argv) { /* "-p <priority> <pid> [...]" */

networking/sendmail.c

@@ -537,7 +537,7 @@ int sendgetmail_main(int argc ATTRIBUTE_UNUSED, char **argv)
 		// NOTE: we don't use xatou(buf) since buf is "nmsg nbytes"
 		// we only need nmsg and atoi is just exactly what we need
 		// if atoi fails to convert buf into number it returns 0
-		// in this case the following loop simply will not be executed 
+		// in this case the following loop simply will not be executed
 		nmsg = atoi(buf);
 		if (ENABLE_FEATURE_CLEAN_UP)
 			free(buf-4); // buf is "+OK " away from malloc'ed string

printutils/lpd.c

@@ -10,37 +10,40 @@
 /*
  * A typical usage of BB lpd looks as follows:
  * # tcpsvd -E 0 515 lpd SPOOLDIR [HELPER-PROG [ARGS...]]
- * 
+ *
- * This means a network listener is started on port 515 (default for LP protocol). 
+ * This means a network listener is started on port 515 (default for LP protocol).
  * When a client connection is made (via lpr) lpd first change its working directory to SPOOLDIR.
- * 
+ *
- * SPOOLDIR is the spool directory which contains printing queues 
+ * SPOOLDIR is the spool directory which contains printing queues
  * and should have the following structure:
- * 
+ *
  * SPOOLDIR/
  * 	<queue1>
  * 	...
  * 	<queueN>
- * 
+ *
  * <queueX> can be of two types:
  * 	A. a printer character device or an ordinary file a link to such;
  * 	B. a directory.
- * 
+ *
- * In case A lpd just dumps the data it receives from client (lpr) to the 
+ * In case A lpd just dumps the data it receives from client (lpr) to the
  * end of queue file/device. This is non-spooling mode.
- * 
+ *
- * In case B lpd enters spooling mode. It reliably saves client data along with control info 
+ * In case B lpd enters spooling mode. It reliably saves client data along with control info
- * in two unique files under the queue directory. These files are named dfAXXXHHHH and cfAXXXHHHH, 
+ * in two unique files under the queue directory. These files are named dfAXXXHHHH and cfAXXXHHHH,
- * where XXX is the job number and HHHH is the client hostname. Unless a printing helper application 
+ * where XXX is the job number and HHHH is the client hostname. Unless a printing helper application
  * is specified lpd is done at this point.
- * 
+ *
+ * NB: file names are produced by peer! They actually may be anything at all!
+ * lpd only sanitizes them (by removing most non-alphanumerics).
+ *
  * If HELPER-PROG (with optional arguments) is specified then lpd continues to process client data:
- * 	1. it reads and parses control file (cfA...). The parse process results in setting environment 
+ * 	1. it reads and parses control file (cfA...). The parse process results in setting environment
- * 	variables whose values were passed in control file; when parsing is complete, lpd deletes 
+ * 	variables whose values were passed in control file; when parsing is complete, lpd deletes
  * 	control file.
- * 	2. it spawns specified helper application. It is then the helper application who is responsible 
+ * 	2. it spawns specified helper application. It is then the helper application who is responsible
  * 	for both actual printing and deleting processed data file.
- * 
+ *
  * A good lpr passes control files which when parsed provide the following variables:
  * $H = host which issues the job
  * $P = user who prints
@@ -49,13 +52,17 @@
  * $L = print banner page
  * $M = the user to whom a mail should be sent if a problem occurs
  * $l = name of datafile ("dfAxxx") - file whose content are to be printed
- * 
+ *
+ * lpd also provides $DATAFILE environment variable - the ACTUAL name
+ * of the datafile under which it was saved.
+ * $l is not reliable (you are at mercy of remote peer), DON'T USE IT.
+ *
  * Thus, a typical helper can be something like this:
  * #!/bin/sh
  * cat "$l" >/dev/lp0
  * mv -f "$l" save/
- * 
  */
+
 #include "libbb.h"
 
 // strip argument of bad chars

printutils/lpr.c

@@ -49,7 +49,7 @@ int lpqr_main(int argc ATTRIBUTE_UNUSED, char *argv[])
 		OPT_U           = 1 << 1, // -U username
 
 		LPR_V           = 1 << 2, // -V: be verbose
-		LPR_h           = 1 << 3, // -h: want banner printed    
+		LPR_h           = 1 << 3, // -h: want banner printed
 		LPR_C           = 1 << 4, // -C class: job "class" (? supposedly printed on banner)
 		LPR_J           = 1 << 5, // -J title: the job title for the banner page
 		LPR_m           = 1 << 6, // -m: send mail back to user

shell/msh.c

@@ -2740,7 +2740,7 @@ static int forkexec(struct op *t, int *pin, int *pout, int no_fork, char **wp)
 	// longjmps away (at "Run builtin" below), leaving t->op_words clobbered!
 	// See http://bugs.busybox.net/view.php?id=846.
 	// Now we do not touch t->op_words, but separately pass wp as param list
-	// to builtins 
+	// to builtins
 	DBGPRINTF(("FORKEXEC: bltin %p, no_fork %d, owp %p\n", bltin,
 			no_fork, owp));
 	/* Don't fork if it is a lone builtin (not in pipe)

util-linux/script.c

@@ -168,7 +168,7 @@ int script_main(int argc ATTRIBUTE_UNUSED, char **argv)
 	/* child: make pty slave to be input, output, error; run shell */
 	close(pty); /* close pty master */
 	/* open pty slave to fd 0,1,2 */
-	close(0);               
+	close(0);
 	xopen(pty_line, O_RDWR); /* uses fd 0 */
 	xdup2(0, 1);
 	xdup2(0, 2);

util-linux/volume_id/get_devname.c

@@ -71,7 +71,7 @@ static void
 uuidcache_addentry(char *device, /*int major, int minor,*/ char *label, char *uuid)
 {
 	struct uuidCache_s *last;
-    
+
 	if (!uuidCache) {
 		last = uuidCache = xzalloc(sizeof(*uuidCache));
 	} else {